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The Open Dentistry Journal, 2016, 10, 148-157

The Open Dentistry Journal Content list available at: www.benthamopen.com/TODENTJ/ DOI: 10.2174/1874210601610010148

Effect of CO2, Nd:YAG and Er:YAG Lasers on Microtensile Bond Strength of Composite to Bleached-Enamel Mahshid Mohammadi Basir1, Mohammad Bagher Rezvani1, Nasim Chiniforush2 and Zohreh Moradi3,* 1

Department of Operative Dentistry, Shahed University, Tehran, Iran Laser Research Center of Dentistry, Tehran University of Medical Sciences, Tehran, Iran 3 Department of Operative Dentistry, Tehran University of Medical Sciences, Tehran, Iran 2

Received: September 27, 2015

Revised: November 17, 2015

Accepted: December 29, 2015

Abstract: Background: Tooth restoration immediately after bleaching is challenging due to the potential problems in achieving adequate bond strength. Objective: The aim of this study was to evaluate the effect of surface treatment with ER:YAG, ND:YAG, CO2 lasers and 10% sodium ascorbate solution on immediate microtensile bond strength of composite resin to recently bleached enamel. Materials & Methods: Ninety sound molar teeth were randomly divided into three main groups (n:30) : NB (without bleaching), HB (bleached with 38% carbamide peroxide) and OB (bleached with Heydent bleaching gel assisted by diode laser). Each group was divided into five subgroups (n:6) : Si (without surface treatment), Er (Er:YAG laser), CO2 (CO2 laser), Nd (Nd:YAG laser) and As (Immersion in 10% sodium ascorbate solution). The bonding system was then applied and composite build-ups were constructed. The teeth were sectioned by low speed saw to obtain enamel- resin sticks and submitted to microtensile bond testing. Statistical analyses were done using two- way ANOVA, Tukey and Tamhane tests. Results: µTBS of bleached teeth irradiated with ND:YAG laser was not significantly different from NB-Nd group. Microtensile bond strength of OB-Er group was higher than NB-Er and HB-Er groups. The mean µTBS of HB-CO2 group was higher than NB-CO2 group; the average µTBS of HB-As and OB-As groups was also higher than NB-As group. Conclusion: Use of Nd:YAG, CO2 lasers and 10% sodium ascorbate solution could improve the bond strength in home-bleached specimens. Application of ND:YAG laser on nonbleached specimens and Er:YAG laser on office-bleached specimens led to the highest µTBS in comparison to other surface treatments in each main group. Keywords: Bleaching, CO2 laser, Er:YAG laser, microtensile bond strength, Nd:YAG laser, sodium ascorbate.

* Address correspondence to this author at the Department of Operative Dentistry, Tehran University of Medical Sciences, Tehran, Iran; Tel: +982188015017; Fax: +982188015017; E-mail: [email protected]

1874-2106/16

2016 Bentham Open

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INTRODUCTION Esthetic dentistry is usually a combination of bleaching treatment and subsequent tooth-colored restorations [1]. A reduction in bond strength of adhesive restorations to enamel and dentin immediately after bleaching has been reported in the literature [2 - 4]. It appears that oxygen free radicals present in tooth structure prevent the polymerization of adhesives and composite resins [5]. Also, bleaching causes morphological alterations in enamel and dentin that include loss of calcium and phosphate, loss of prismatic enamel structure, destruction of organic matrix and accumulation of oxygen in dentin [6]. Therefore, textbooks recommend a one to two week interval between the bleaching and restorative treatments in order to obtain adequate bond strength [7, 8]. This time interval prolongs the course of treatment and increases the risk of crown fracture, microleakage and secondary discoloration in cases with intracoronal bleaching. These complications are unfavorable to both the patient and dentist [9]. Antioxidant agents such as 10% sodium ascorbate and catalase enzyme have been used to reverse this process. However, these agents are not routinely used in the clinical procedures [10, 11]. Appearance of new technologies such as laser beams has been associated with undeniable benefits in dentistry. ND:YAG and Er:YAG lasers are used in operative dentistry for the removal of carious lesion, conditioning of tooth surfaces and enamel and dentin surface treatment in order to minimize marginal microleakage and increase the bond strength [11 - 15]. Enamel is a solid opaque substance with the ability to absorb CO2 laser beams. Physical changes due to the irradiation of this type of laser include melting and recrystallization [16]. Considering the ablative effect of Er:YAG laser on tooth structure and the recrystallization effect of ND:YAG and CO2 lasers, it seems that application of these lasers after tooth bleaching can cause a temperature rise in tooth structure and subsequent morphological changes in enamel and dentin leading to the elimination of remaining free radicals and rapid neutralization of the adverse effects of bleaching agents on bond strength [11, 17]. Table 1. Distribution of experimental groups. Group number

Group name

Type of surface treatment

Group 1

NB-Si

No bleaching

Group 2

NB-As

No bleaching + sodium ascorbate

Group 3

NB-Er

No bleaching + Er:YAG laser

Group 4

NB-Nd

No bleaching + ND:YAG laser

Group 5

MB-CO2

No bleaching + CO2 laser

Group 6

HB-Si

Home bleaching

Group 7

HB-As

Home bleaching + sodium ascorbate

Group 8

HB-Er

Home bleaching + Er:YAG laser

Group 9

HB-Nd

Home bleaching + ND:YAG laser

Group 10

HB-CO2

Home bleaching + CO2 laser

Group 11

OB-Si

Office bleaching

Group 12

OB-As

Office bleaching + sodium ascorbate

Group 13

OB-Er

Office bleaching + Er:YAG laser

Group 14

OB-Nd

Office bleaching + ND:YAG laser

OB-CO2 Office bleaching + CO2 laser Group 15 Abbreviations: NB, No Bleaching; HB, Home Bleaching; OB, Office Bleaching; Si, Single Bond 2; Nd, ND:YAG Laser; Er, Er:YAG Laser; CO2, CO2 Laser; As, Sodium Ascorbate.

Due to the lack of adequate information on this subject, controversial results obtained by previous studies and scarce data on the effect of CO2 laser in this respect, the aim of the present study was to evaluate the effects of ND:YAG, Er:YAG and CO2 lasers on microtensile bond strength of recently bleached enamel to composite resin and comparison of the obtained results with the conventional method of 10% sodium ascorbate (antioxidant) application. MATERIALS AND METHODS: Selection and Preparation of Teeth: A total of 90 extracted human third molars with no fracture or carious lesions were used in this study. Organic debris and tissue remnants were removed prior to the study using periodontal scaler. Prophylaxis was done with the

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fluoride-free pumice and rubber cup. The teeth were disinfected with 0.5% chloramine solution (Chloramine T Trihydrate, Merck, Schuchardt, Germany) for one week and stored in distilled water at 4˚C until one week prior to the test and then immersed in artificial saliva (ISO/TS 11405) and stored in an incubator (Kavoosh MEGA ,Tehran, Iran) at 37°C until testing. The composition of artificial saliva was 1.5 mmol/L Ca+2, 50 mmol/L KCl, 0.9 mmol/L PO4-3, and 20 mmol/L Trihydroxy methylaminomethane, with a pH of 7.0. The artificial saliva was refreshed daily. It was saturated with calcium and phosphate ions similar to the composition of human saliva [1]. The teeth were evaluated under stereomicroscope (Nikon C-DS, Tokyo, Japan) at 50X magnification for exclusion of samples with cracks or hypoplastic lesions. In order to standardize the texture of the surface and smear layer, buccal surfaces of teeth were ground by 600 grit silicon carbide sandpapers for 60 seconds under running water (ISO/TS 11405). Samples were randomly divided into three main groups of 30 samples each based on the type of bleaching treatment (Home or Office) and the third group was considered as the control group and did not undergo bleaching. Each group was categorized into 5 subgroups of 6 specimens each to provide totals 270 stick samples for microtensile bond strength test. This implies n=18 for each group (Table 1). Control Group (NB)(n=30): Specimens in this group did not undergo bleaching treatment and stored in distilled water at 4°C and then immersed in artificial saliva one week before the bonding procedure. Home Bleaching Group (HB)(n=30): Home bleaching was carried out using 38% carbamide peroxide gel (Discus Dental, CA, USA) applied in 2 mm thickness on tooth surfaces for 15 minutes. The teeth were placed in Petri dish containing artificial saliva in a way that their buccal halves were out of the saliva and in contact with the gel. Petri dishes were stored in an incubator at 37°C for 15 minutes. The gel was then washed off the teeth and the abovementioned procedures were repeated. Therefore, the teeth were bleached for a total of 30 minutes, according to manufacturer’s instructions. After completion of the mentioned 30 minute period, the teeth were placed in a test tube containing 14 ml of artificial saliva and stored in an incubator at 37°C. Artificial saliva was refreshed daily and the whole duration of treatment was three weeks. Office Bleaching Group (OB)(n=30): Office bleaching was done using Heydent JW Power Bleaching Gel (Production of Farafan Diagnostics Co , under license of Heydent, Germany Tehran- Iran) in two treatment sessions. Each session included three times application of gel. JW Powder was mixed with 30% hydrogen peroxide. The prepared gel was then applied to tooth surfaces in 1.5 mm thickness and activated with CHEESE ™ (Wuhan Gigaa Optronics Technology Co, LTD, China) 810 nm diode laser in continuous mode with power of 1W, exposure time of 30 seconds and irradiation distance of 6 mm from the gel surface. Gel was remained on tooth surfaces for one minute. During this time period, the teeth were maintained in the Petri dish containing artificial saliva in a way that their buccal halves were out of the saliva and in contact with gel. Petri dishes were placed in an incubator at 37°C. The gel was then washed off the tooth surfaces. This process was repeated three times. The teeth were then rinsed, placed in a test tube containing 14 ml of artificial saliva and stored in an incubator at 37°C. Artificial saliva was refreshed daily. The second session was scheduled one week later during which the abovementioned procedures were repeated. Experimental Groups: The experimental groups included three main groups with 5 different surface treatments. In total, the experiment was conducted on 15 experimental groups based on the type of bleaching and surface treatment method. Groups 1, 6 and 11 (Si): No surface treatment performed. Groups 2, 7 and 12 (As): 10 ml of 10% sodium ascorbate solution was poured on tooth surfaces at a speed of 1 ml/min. This solution was agitated to enamel surfaces continuously for 10 minutes and then rinsed with distilled water and air-dried. Groups 3, 8 and 13 (Er): Irradiation with Er:YAG laser (USD20, DEKA Dental laser systems, Florence, Italy) with

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energy of 50 mJ, frequency of 10 Hz and power of 0.5 W, pulse duration of 230 µs (very short pulse) and non-contact mode at distance of 4 mm that provides 1 mm beam diameter. In order to standardize the 4 mm irradiation distance between the laser hand piece and the respective surface, an endodontic k-file was fixed to the hand piece. All the area of enamel was irradiated uniformly by hand in grid pattern by a single operator for 60 sec. Groups 4, 9 and 14 (Nd): Irradiation with Nd:YAG laser (FIDELIS, Fotona , Slovenia) using power of 1 W, frequency 10 Hz, pulse duration : 100 μS (very short pulse) and contact mode in grid pattern via a 300 μm fiber optic cable by single operator manually for 60 sec. Groups 5, 10 and 15 (CO2): Irradiation with CO2 laser (US- 20D , DEKA Dental laser systems, Florence, Italy) at power of 0.5 W, frequency 10 Hz, pulse duration of 1.5 ms, non-contact mode at distance of 12.5 mm providing beam diameter of 1 mm manually by one operator in grid pattern for 60 sec. The fiber optic cable in this type of laser has an outer sheath that keeps a 12.5 mm distance from the respective area. Before the bonding procedure, one sample from each group was selected for evaluation of surface alterations by FESEM (S4160 Hitachi, Japan). Sample preparation for electron microscopic evaluation included fixation, dehydration, chemical drying and gold coating. After these treatments, the bonding system was used according to the manufacturer’s instructions. All the specimens were etched with 35% phosphoric acid (Scotch Bond Etchant, 3MESPE, St. Paul, MN, USA) for 15 s, rinsed for 10 s and air dried for 5 s with air spray. Adper Single Bond 2 adhesive (3MESPE , St. Paul , MN , USA) was applied in two coats and air-dried for 5 s with compressed air in order for the solvent to vaporize and cured for 10 s with LED light curing unit (800 mW/cm2) (DEMI, Kerr, Ca, USA). Z250 composite resin was applied in two layers to the entire buccal surface. Each layer was cured for 20 s with the LED light-curing unit. Finally, the composite build-up was cured for 100 s from different directions. Microtensile Bond Strength Testing: After the bonding procedure, samples were stored in artificial saliva in an incubator at 37°C for 24 hours. The teeth were then embedded in auto-polymerizing acrylic resin (Meliodent, Heraeuse Kulzer, Germany) and sectioned in X and Y directions with a slow speed diamond saw (Mecatome, T201A, France) along with water coolant. Three rectangularshaped enamel-resin sticks were obtained from each tooth as such with a mean cross section of 1 mm2. A digital caliper to the nearest 0.01 mm (Mitutoyo, Tokyo, Japan) was used for the accurate measurement of the dimensions of sticks. In general, 18 sticks in each experimental group and a total of 270 sticks in 15 experimental groups were prepared. Sticks were attached to a microtensile tester (Microtensile Tester, Bisco, Schaumburg, IL, USA) using cyanoacrylate glue (Mitreaple, Turkey) and subjected to microtensile testing at a crosshead speed of 1 mm/min. Microtensile bond strength in MPa was calculated by dividing the exerted force in Newton at the time of fracture by the cross sectional area of enamel/resin interface in mm2 measured before the failure. Failure Mode Analysis: Failure mode was determined using a stereomicroscope (Nikon C-DS, Tokyo, Japan) with 50X magnification. Failure mode of samples was categorized as follows: Adhesive failure: Fracture at the tooth/adhesive or composite/adhesive interface in more than 75% of the understudy areas. Cohesive failure in resin: This fracture occurs mainly in the composite resin in a way that more than 75% of the bonding area has been covered with the restorative material. Cohesive failure in tooth: Fracture mainly occurs in the tooth structure. Mixed failure: Mixed fracture is a combination of the abovementioned fractures. Statistical Analysis: The prematurely debonded specimens were included in the tooth mean and microtensile bond strength of these samples was considered zero. Data obtained from microtensile bond strength testing were analyzed using portable SPSS PASW 18 software. Considering the normal distribution of data, two-way ANOVA was applied to assess the interaction of the effect of bleaching with type of surface treatment. P

Effect of CO2, Nd:YAG and Er:YAG Lasers on Microtensile Bond Strength of Composite to Bleached-Enamel.

Tooth restoration immediately after bleaching is challenging due to the potential problems in achieving adequate bond strength...
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